Interactive training and educational systems today, such as the one disclosed in U.S. Pat. No. 4,701,130, typically employ tape players for providing audio instructions to the student as he or she works with an application program running on the central processing unit (CPU) of a computing device. The tape is played directly through an adjoining speaker with no intervention by the CPU required to generate audio instructions. This allows the CPU to run the application program with few interruptions. Interruptions in great number slow down the execution of the application program since the CPU cannot efficiently handle both tasks simultaneously.
A drawback of using a tape player, however, is analog format in which instructions are stored. Analog data requires more space and takes longer to access than data stored on a digital storage device. Training for complex application programs may require multiple tapes as well as digital storage media such as floppy disks containing the training program. The task of switching tapes, loading floppy disks and operating the tape recorder is bothersome and difficult. Any tutorial program that accompanies the instructions must be provided on the separate floppy disks because of the slow data transfer from tape.
Although the use of tape to provide instructions is adequate, the analog data format has limitations that are not present if the data were digital. Such data stored in a digital format can be easily manipulated within a computing device. It can be copied and stored along with other computer programs and data. It can be compressed and decompressed so that it takes less space while stored. It can be transmitted across computer networks already in place. It provides far better storage and playback quality than analog data. Special effects may be carried out with digital data. For example, one can add and echo, vary the pitch, brighten an image, or sharpen or blur a focus using a conventional computing device.
Digital data storage devices can also store far much more data than analog devices such as tape recorders. Current optical data drives--both read only and erasable--are available at relatively low cost and can store on a single disc or equivalent media the contents of a number of tapes.
One possible solution is to use a compact disc audio (CD) player in place of the tape player. Compact discs, which are the data storage medium played on a CD player, can store immense amounts of digital data. CD players include hardware for producing sound through an adjoining speaker, just as is presently done with a tape player. But because of the "red book" data format used with present CD players, they provide only an hour of output in the form of high fidelity sound. That format requires over 44,000 samples per second of sound, with two bytes of digital data per sample.
Another possible solution is to use a hard disk drive or a CDROM drive. A CDROM drive uses a different type of disc called a CDROM disc which provides the same digital data storage capabilities as a hard disk drive. CDROM drives are not limited to the "red book" audio standard but can also store and transfer raw digital data. This data could be digitized sound data that has been sampled at a lower rate than the 44.1 kHz standard of red book audio. This allows the storage of more than an hour of digitized sound on a single CDROM disc, at a reduced sound quality.
Unlike the tape recorder or the CD player, however, a digital data storage device must pass its digital data into a computing device. The digital data read into the computer can then be sent to an audio device or a video device that matches the digital data representation. This constraint affects the computing device's ability to effectively provide audio instructions concurrently with running of an application program for two reasons. First, as mentioned, transferring data from the digital data storage device to the audio or video device to generate sound or to display visual effects consumes a large amount of CPU time. This affects the CPU's ability to run an independent application program without significant interruption. Secondly, the application program may interrupt the CPU to access a disk drive, while the CPU is attempting to transfer the audio or video data. This interruption causes gaps in the audible words known as "dropouts" and also produces audible noise. Simultaneous access to the drive and generating sustained sound are difficult since both tasks use the CPU.